Cognitive aging in women is closely related to age-related changes in neuroendocrine systems, particulariy the loss of circulating ovarian steroid hormones that occurs in menopause. Surprising findings from the Women's Health Initiative Memory Study showed that hormone treatment (HT) begun long after the onset of menopause failed to improve cognition and may have been harmful. This contrasts with other studies indicating beneficial cognitive effects of HT begun soon after the onset of menopause. To reconcile these findings a 'window of opportunity' hypothesis has been proposed, such that there is a limited period of fime after menopause during which HT may improve cognifion. Because of other health risks associated with long-term HT including cardiovascular disease and cancer, current advice is for women to take a short course of HT at the onset of menopause and then disconfinue it. We will test, in a well-characterized animal model, whether beneficial cognitive effects of HT (on spatiotemporal working memory, visual recognition memory, and vulnerability to distraction) persist after discontinuation of HT, and whether they are sfill observed when HT is begun after a long delay post-menopause. In vivo neuroimaging analyses conducted concurrently with behavioral tesfing will measure neurobiological changes in parallel with cognitive ability. This study will test the 'window of opportunity' hypothesis explicitly, as well as whether cognitiye benefits can be maintained after withdrawal of HT. These studies will provide critical translational insights into how HT can improve cognitive outcomes of aging. RELEVANCE (See instructions): Hormone replacement therapy in women after menopause can improve brain funcfion, including memory. We will test, in an animal model, how the fiming of hormone therapy after menopause affects its ability to improve brain function, both in terms of whether therapy must begin soon after menopause to be effective, and whether its beneficial effects persist after therapy is discontinued. These studies will help us maintain best brain and memory function in women as they age.